Rapid advances are occurring in various electronic devices especially display devices that are used for various communication, financial, capture, and archival purposes. For such uses as touch screen panels, electrochromic devices, light emitting diodes, field effect transistors, and liquid crystal displays, electrically-conductive films are essential and considerable efforts are being made in the industry to improve the properties of those electrically-conductive films as well as methods for making them.
In addition, as the noted display devices have developed in recent years, their attraction has increased greatly with the use of touch screen technology whereby light touches on the screen surface with a finger or stylus can create signals to cause changes in screen views or cause the reception or sending of information, telecommunications, interaction with the Internet, and many other features that are being developed at an ever-increasing pace of innovation. Touch screen technology has been made possible largely by the use of transparent electrically-conductive grids on the primary display so that the location of the noted touch on the screen surface can be detected by appropriate electrical circuitry and software.
Currently, most touch screen displays use Indium Tin Oxide (ITO) coatings to create arrays of capacitive areas used to distinguish multiple point contacts. ITO coatings have significant disadvantages. Indium is an expensive rare earth metal and is available in limited supply from very few sources in the world. ITO conductivity is relatively low and requires short line lengths to achieve adequate response rates. Touch screens for large displays are broken up into smaller segments to reduce the conductive line length to an acceptable resistance. ITO is a ceramic material, is not readily bent or flexed, and requires vacuum deposition with high processing temperatures to prepare the electrically-conductive layers.
Silver is an ideal conductor having conductivity 50 to 100 times greater than ITO. Silver is used in many commercial applications and is available from numerous sources. It is highly desirable to make electrically-conductive film elements using silver as the source of conductivity, but it requires considerable development or other processing operations to obtain the optimal electrically-conductive properties.
U.S. Patent Application Publication 2011/0308846 (Ichiki) describes the preparation of electrically-conductive films formed by reducing a silver halide image in electrically-conductive networks with silver wire sizes less than 10 μm, which electrically-conductive films can be used to form touch panels in displays.
In addition, U.S. Pat. No. 3,464,822 (Blake) describes the use of a silver halide emulsion in a photographic element to form an electrically-conductive silver surface image by development and one or more treatment baths after development.
U.S. Pat. No. 7,829,270 (Nakahira) describes the use of photosensitive silver halide materials to form electrically-conductive silver metal patterns. After exposure of the photosensitive silver halide materials, they are processed using a black-and-white development solution followed by fixing and physical development and electroless plating operations.
Moreover, U.S. Pat. No. 8,012,676 (Yoshiki et al.) also describes similar processes but further including operations to enhance electrical conductivity of the resulting silver metal images.
Thus, it is known to provide electrically-conductive silver patterns on transparent films using various processing solutions and conditions. However, there is a further need to improve the electrical conductivity of silver patterns, especially silver patterns in the form of fine lines without increasing Dmin. That is, there is a need to balance improved silver metal conductivity, increased transparency, and low Dmin in electrically-conductive silver images. It with these needs in mind, that the present invention was discovered.